It is well known in the art that brazing of aluminum parts can be performed utilizing fluxes based on alkali metal fluoroaluminates. Fluxes of this type are generally considered to be noncorrosive. See for example, U.S. Pat. No. 3,971,501 which applies a flux based on KAlF4 and K3AlF6, or U.S. Pat. No. 4,689,092 which applies a flux based on potassium fluoroaluminate and cesium fluoroaluminate. U.S. Pat. No. 6,949,300 discloses kinetic spraying onto metal substrates a brazing composition that comprises corrosion protector, brazing filler and/or non-corrosive flux.
If contacted for extended times with water or aqueous liquids, aluminum parts brazed with potassium fluoroaluminate based fluxes show signs of corrosion. This is disclosed by Bo Yang et al. in Journal of ASTM International, Vol. 3, Issue 10 (2006). The corrosion can be recognized by the appearance of turbidity in the water or liquid and seems, for example, to induce the formation of aluminum hydroxide. This corrosion seems to be caused by fluoride ions which are leached from brazing residues if the brazed parts are in contact with water for extended periods of time, e.g., for at least one day or longer.